aurora borealis,The lights are at their most frequent in late autumn and winter/early spring. Between the autumn equinox and spring equinox (21 September - 21 March), it is dark between 6 pm and 1 am, and you have maximum chances of spotting the lights. However, the weather is also of importance, and September, October and November tend to be wet and snowless in the north.
From December the weather dries up, and there is normally plenty of snow. If you come in December or January, you experience the polar nights with atmospheric evenings and very short days.